1. Field of the Invention
The present invention relates to a shared image scanning method and picture scanner thereof, and more particularly to a shared image scanning method and picture scanner that shares a document to a plurality of image areas, then construct the images to a whole document image signal The picture scanner is formed and is with features of fast scan and enhancing the scanning quality.
2. Description of the Related Art
In recent years, scanners, particularly picture scanners become one of the major computer peripherals, and picture scanners can capture the image of a document, a textual page, a picture, a film or even a planar object. In an image capturing method, a light is projected onto the document first. Further, a sensor such as a charge-coupled device (CCD) or a contact image sensor (CIS) is provided for converting the reflected light into a image signal, then a scanning software is provided for the image signal to form a image signal, and the image signal can be stored in an image file with a format of TIFF, EPS, BMP, GIF and PCX, etc. Since the document usually comes with areas of different brightness, the intensity of the reflected lights in different areas of the document varies; different types are developed to enhance the shortage. Commercialized scanners are divided into three types: a flat-bed scanner, a transparent media adapter scanner and a drum scanner.
The flat-bed scanner is used for scanning pictures, documents or printed matters. In a scanner has a transparent plate made of glass or plastics and installed on the top of scanner for placing a desired scanning document, a CCD module (CCDM) for sensing component moves along a track to scan the document row by row (called, sequence line scanning) and converts the image of the document into a digital data. The flat-bed scanner is the most frequently used in application of simple document. Other scanners manufactured by the similar principle of the aforementioned scanner based on the relative movement of the document and the CCDM include handheld scanners and sheetfed scanners.
In the transparent media adapter scanner, a mask is installed on the scanner for uniformly projecting a light source to scan a script such as a transparency and a film.
The drum scanner adopts a photomultiplier tube (PMT) as a light sensing device. The PMT technology can focus bright light beams at a very small area of a picture at one time, such that the drum scanner exposed all layers to be shown in a dense area of the original script. The drum scanner is used mainly in large picture, engineering drawing or professional advertising and picture producing companies.
With reference to FIGS. 1 and 2 for a perspective view and a cross-sectional view of a conventional flat-bed scanner respectively, the scanner comprises: a frame 11, a transparent plate 12, an image sensing module 13 and two guide tracks 14. The transparent plate 12 is installed at the top of the frame 11, and a document 15 is placed on the top of the transparent plate 12. The guide track 14 is installed on both sides inside the frame 11 for guiding and moving the image sensing module 13. The image sensing module 13 includes a light source which can be a xenon lamp or a cold cathode fluorescent lamp (CCFL) 131, a reflective base 132, a cylindrical lens 133, a line image sensor 134 and a printed circuit board 135. The cold cathode fluorescent lamp 131 is used for projecting a light source. The reflective base 132 is used for collecting and focusing the light emitted from the cold cathode fluorescent lamp 131 onto a document 15. The cylindrical lens 133 is used for focusing the light source onto the line image sensor 134. The printed circuit board 135 is carried by and electrically coupled to the line image sensor 134. For different line image sensors 134, a linear CCD image sensor or a contact image sensor (CIS) is used. In the selection of these two types of image sensors, the CCD technology is well developed and has the features of less noise, plentiful color, profound depth of field, and capability of scanning a piece paper with folded lines. However, the CIS including the CMOS image sensor featuring a simple manufacturing procedure and a small thickness for manufacturing a super thin scanner, and having the drawbacks of a shallower depth of field, and the requirement of a flat scanned draft, incapability of scanning 3D objects, and a poor noise resistance that affects the image quality of the document.
When a document 15 is scanned, a step motor is used for driving and moving the guide track 14, such that the guide track 14 drives and moves the image sensing module 13 in a scanning direction for the image sensing module 13 to scan the document 15. However, the drawback of such conventional scanner resides on that the guide track 14 needs to drive and move the image sensing module 13 towards the scanning direction to complete scanning a whole copy of the document 15, and thus causing a low scanning speed. Since gears of the step motor are engaged for driving and moving the guide track 14 and the image sensing module 13, vibrations may occur due to a low tolerance or precision, and the document 15 cannot be detected accurately such that a poor image quality may result. In the present product development, the optical resolution of the image sensing module 13 refers to the number of image points captured by the light sensing device per inch, and the optical resolution can be up to 2400 dpi. As to a product with an acceptable price in the market, the mechanical resolution of the step motor and the guide track 14 refers to the number of steps moved by the step motor of the light sensing device per inch is lower than 1200 dpi. Contrarily, if the step motor is driven by a high precision ball bearing, the resolution can be simulataneous improvement, but it also incurs a higher cost. Therefore, the present manufacturing technology cannot match the optical resolution with the mechanical resolution, and the actual image resolution cannot be improved further.
The conventional flat-bed scanner has another drawback that the design of present scanners tends to be light, thin, short and compact, and thus the distance between the document 15 and the line image sensor 13 is too small, and the field of view (FOV) becomes larger. If the document 15 has a folded line, then the document 15 with the folded line will have a focus deviation and an image of the document cannot be formed accurately on the line image sensor 134, thus blurred the document image.
Since the scanning method using a guide track to drive a light sensing device still has limitations, Japan Patent No. JP 1186077 discloses a method of using five CCD image sensors to capture an image of a document by dividing the documents into several areas. However, if such technology is applied to a scanner, the CCD image sensors and an image forming lens must be maintain at a long distance from the target document 15, so that the image forming lens can focus a document image onto the image sensors, and the thickness of the scanner must be very thick and does not meet the user requirements. Similarly, once an image forming lens of a wide angle short back focal length is used, the image distance can be shortened, but the depth of field will be insufficient. In a scanner as disclosed in Japan Patent No. JP6098098, the document image is refracted, and different image areas form images onto image sensors by a plurality of image forming lenses. However, such patented technology still has the issue of mechanical resolution with respect to the movement of the document and the image sensor.
As the image sensor advances, the area image sensor can capture a whole picture with two-dimension in each exposure time. For applications, it is not necessary to move the the document or the sensor to facilitate applying the image sensor to the scanner. In recent years, the price of the area image sensor drops drastically, and the area image sensor can be applied extensively to the scanner.